JP7083710B2 - Method for manufacturing metal particle dispersion, metal particle dispersion, and method for manufacturing coated substrate - Google Patents

Description

The present invention relates to a method for producing a metal particle dispersion liquid useful for a conductive material or the like.

Metal particles are used for various purposes as catalyst materials, semiconductor materials, conductive materials and the like. For example, the conductive material is used for electrodes, circuits, antistatic transparent coatings, electromagnetic wave shielding transparent coatings, capacitor electrodes and the like of various electronic devices (see Non-Patent Document 1).

As a method for producing such metal particles, a method for producing metal particles by reducing a metal salt in an organic solvent has been proposed (see, for example, Patent Documents 1 and 2). However, the metal particles obtained by the method using this organic solvent have a problem of low conductivity.

Therefore, in order to obtain metal particles having higher conductivity, it is also attempted to produce a metal particle dispersion liquid in water. For example, a method has been proposed in which an organic stabilizer is used while an inert gas is circulated in a solvent to provide a citric acid coating layer on metal particles to improve oxidation resistance (see, for example, Patent Document 3). .. However, it is insufficient to suppress the oxidation and ionization of metal particles, and it is difficult to obtain a stable metal particle dispersion. Further, since it is coated with an organic substance, there is a problem that the conductivity is low.

Japanese Unexamined Patent Publication No. 2005-281781 Japanese Unexamined Patent Publication No. 2008-075181 Japanese Unexamined Patent Publication No. 2010-189681

"Science of Metals and Semiconductor Nanoparticles" Author / Chemical Society of Japan, Publisher / Ryosuke Sone, Publisher / Kagaku-Dojin (2012)

An object of the present invention is to provide a metal particle dispersion having high conductivity and high storage stability.

A metal salt reduction reaction (particle preparation step) is carried out in a liquid containing fine bubbles having an average bubble diameter of 40 nm to 10 μm and not containing an organic stabilizer. Next, the metal particles obtained by reducing the metal salt are washed with a cleaning liquid to remove the salt (cleaning step), thereby suppressing the oxidation and ionization of the metal particles and dramatically improving the storage stability (storing stability). A metal particle dispersion (prolonged) can be obtained.

By using a liquid containing these fine bubbles during the reduction reaction of the metal salt, the metal particles do not aggregate even without an organic stabilizer, and the dispersibility of the particles is high and the storage stability is high. It was found that a liquid was obtained. Furthermore, it has been found that this liquid does not contain an organic stabilizer, and the metal particles of the coated substrate using the obtained dispersion liquid are not coated with an organic substance, so that they exhibit high conductivity performance.

It is possible to obtain a metal particle dispersion having high storage stability in which oxidation and ionization of metal particles are suppressed. Further, the coated base material using this metal particle dispersion liquid exhibits high conductivity performance.

In the method for producing a metal particle dispersion liquid of the present invention, a metal salt is reduced in a liquid containing fine bubbles (micro-nano bubbles) and not containing an organic stabilizer (hereinafter, may be referred to as a reaction liquid) to reduce the metal particles. It has a particle preparation step for preparing the particles and a cleaning step for cleaning the metal particles prepared in the particle preparation step with a cleaning liquid.
This manufacturing method may have other steps before and after each of the above steps. For example, after the cleaning step, there may be a coarse particle removing step of removing the coarse particles.

The liquid containing microbubbles (including the bubbling liquid containing microbubbles) used in the present invention has a higher dissolved oxygen concentration and a higher redox potential than the conventional degassed (deoxidized) treated water with an inert gas. For this reason, the use of a liquid containing fine bubbles is a condition for being more easily oxidized, and it is generally considered unfavorable to use the liquid containing fine bubbles in the reduction reaction. Further, the organic stabilizer has a function of adsorbing to a metal salt or metal particles to improve dispersion stability. Therefore, in the reduction reaction of the metal salt, if the organic stabilizer is not present, the metal particles are aggregated and the stability of the metal particle dispersion is also lowered, which is generally considered to be unfavorable.
However, surprisingly, when the reduction reaction of the metal salt is carried out using the liquid containing the fine bubbles, the dispersibility of the metal salt is high even in the absence of the organic stabilizer, and the metal particle dispersion liquid is produced. It was found that the metal particles of the above can be obtained in a high yield, and the dispersibility and storage stability of the metal particles are improved. It was also found that the pot life of the coating liquid using this metal particle dispersion liquid is also improved. Furthermore, it has been found that the coated substrate prepared by using this coating liquid has high conductivity (low surface resistance value). It has been found that this conductivity performance is higher when the organic stabilizer is not used during the reduction reaction in the presence of microbubbles. Although the reason for these is not clear, it is presumed that the microbubbles contained in the reaction solution have a protective effect for the metal particles to exist as a metal without being oxidized. In addition, since the organic stabilizer is not present in the reduction reaction of the metal salt, the organic stabilizer does not adsorb to the metal salt or the metal particles. As a result, it is considered that the conductive performance is improved because the obtained metal particle dispersion liquid, the coating liquid using the same, and the metal particles in the coated base material are not coated with the organic substance derived from the organic stabilizer. ing.

In addition, a liquid containing fine particles should be used in both the liquid in the above-mentioned metal salt reduction reaction (particle preparation step) and the cleaning liquid in the cleaning of the metal particles obtained by reducing the metal salt (cleaning step). It has been found that metal particles can be obtained in a higher yield, the storage stability of the metal particle dispersion is improved, and the pot life of the coating liquid using this metal particle dispersion is further improved.
The method for producing the metal particle dispersion liquid will be described below.

[Manufacturing method of metal particle dispersion]
<Particle preparation process>
In the reaction solution, the reducing agent and the metal salt are mixed to prepare metal particles. The reaction solution may be an organic solvent or water as long as it does not contain an organic stabilizer and contains microbubbles. However, it is more effective in the case of water.
If an oxidizing gas such as oxygen is present in the reaction solution, the metal may be oxidized. Therefore, it is desirable to reduce the oxidizing gas as much as possible in the space in contact with the reaction solution and the reaction solution. This step is preferably performed in a state of being purged with an inert gas such as _N2 gas or a rare gas in order to suppress the mixing of oxidizing gas.
Here, as the oxidizing gas, oxygen, ozone, carbon dioxide gas, nitrogen monoxide, dinitrogen monoxide, nitrogen dioxide, fluorine, chlorine, chlorine dioxide, nitrogen trifluoride, chlorine trifluoride, silicon tetrachloride, difluoride. Examples thereof include oxygen fluoride and perchlorylfluoride.

In the reduction reaction, if the organic stabilizer is present in the reaction solution, the organic stabilizer is adsorbed on the metal salt, so that the dispersibility of the metal salt is improved and the reduction of the metal salt is smoothly performed. Further, the organic stabilizer is adsorbed on the metal particles obtained by reducing the metal salt, and the dispersibility stability of the metal particle dispersion liquid is improved. Therefore, the pot life of the coating liquid using this metal particle dispersion liquid is also improved. However, since the surface of the metal particles is coated with an organic substance, the conductivity of the coating film using the metal particles may be lower than that without the organic stabilizer.
Examples of this organic stabilizer include gelatin, polyvinyl alcohol, polyvinylpyrrolidone, vinyl acetate, polyacrylic acid, and carboxylic acid compounds.

The reaction solution in this step preferably has an oxidation-reduction potential (ORP) of −50 mV or less, more preferably −100 mV or less. The pH is preferably 2.5 to 10.5, more preferably 2.7 to 10.0. By reducing the metal salt within the range of this redox potential and pH, the formation of metal particles is smoothly performed. The reaction temperature is preferably 10 to 80 ° C.

《Micro bubbles》
The microbubbles are preferably microbubbles (micro-nano bubbles) having an average bubble diameter of 40 nm to 10 μm. Such microbubbles include at least one of so-called nanobubbles having a bubble diameter of 40 to 100 nm (0.1 μm) and so-called microbubbles having a bubble diameter of 0.1 to 10 μm, and those containing both are preferable. The upper limit of the average bubble diameter of the fine bubbles is preferably 500 nm, more preferably 350 nm, and even more preferably 200 nm. The lower limit of the average bubble diameter of the fine bubbles is preferably 50 nm, more preferably 60 nm, and even more preferably 65 nm.

The content of microbubbles is preferably 1.0 × 10 ⁶ cells / mL or more, more preferably 1.0 × 10 ⁷ cells / mL or more, and 1.0 × 10 in order to effectively exert the effect of the present invention. ⁸ pieces / mL or more is more preferable. The upper limit is not particularly limited, but 1.0 × 10 ¹¹ pieces / mL is preferable, 5.0 × 10 ¹⁰ pieces / mL is more preferable, and 1.0 × 10 ¹⁰ pieces / mL is further preferable.

The average bubble diameter and the number of bubbles of the fine bubbles are obtained by analyzing the Brownian motion moving speed of the bubbles in the liquid by the nanoparticle tracking analysis method (NTA). For example, it can be measured with "Nanosite NS300" manufactured by Malvern.

The gas forming the fine bubbles is preferably a non-oxidizing gas. Specifically, at least one of nitrogen, hydrogen, and a rare gas is preferable.

《Metal salt》
As the metal salt used as the raw material of the metal particles, the metal salt selected from the 4th group, 5th group, 6th group, 8th group, 9th group, 10th group, 11th group, 13th group, 14th group and 15th group in the periodic table is used. Be done. Examples of the type of salt include chloride salt, nitrate, sulfate, organic acid salt and the like.

Preferred metal elements are Ti in Group 4, Ta in Group 5, W in Group 6, Ru in Group 8, Co, Rh in Group 9, Ni, Pd, Pt in Group 10, and Cu, Ag, Au in Group 11. Examples are Al and In in the 13th group, Sn in the 14th group, and Sb in the 15th group. This production method is also applicable to easily oxidizable metals other than Au and Ag.

《Reducing agent》
A reducing agent is usually used for the reduction reaction in the particle preparation step.
Examples of the reducing agent include ferrous sulfate, NaBH ₄ , hydrazine, hydrogen, alcohol, sodium hypophosphite, LiBH ₄ , LiAlH ₄ , and diborane.

The amount of the reducing agent used varies depending on the reducing property of the metal salt, but is preferably 0.5 to 10 mol, more preferably 1 to 5 mol, with respect to 1 mol of the metal salt. Here, if the reducing agent is less than 0.5 mol with respect to 1 mol of the metal salt, the reduction may be insufficient and the desired metal particles may not be obtained. On the contrary, if the reducing agent exceeds 10 mol with respect to 1 mol of the metal salt, metal particles having a larger particle diameter than necessary may be generated.

<< pH adjuster >>
The reaction solution in the particle preparation step may be adjusted with a pH adjuster so that the pH becomes 2.5 to 10.5 as described above. A mineral acid or an organic acid is suitable as the pH adjuster.
Here, when an organic acid is used, the one having a large molecular weight has a possibility of coating the metal particles with an organic substance, and therefore, the one having a low molecular weight having 1 to 3 carbon atoms is preferable. The amount used is preferably less than 0.5 mol per 1 mol of the metal salt.

<Washing process>
In the cleaning step, the metal particles prepared in the particle preparation step are washed with a cleaning liquid. Here, desalination is performed. This salt is a substance other than the metal particles generated by the reduction treatment of the metal salt, and exists as an ion in the reaction solution. Specific examples thereof include metal ions such as sodium and iron, boron ions, chloride ions, nitrate ions, sulfate ions, and organic acid ions. In this cleaning step, an organic stabilizer that forms a complex with a metal ion such as a carboxylic acid compound may be used. For example, when a reducing agent containing a metal such as ferrous sulfate is used as the reducing agent, the metal ion of the reducing agent and the organic stabilizer form a complex, and the reducing agent can be efficiently removed. Because.

The cleaning liquid is suitable for water or alcohol, and may contain other components. As this cleaning liquid, it is preferable to use at least one of a bubbling liquid from which oxygen has been removed by bubbling an inert gas in advance and a liquid containing microbubbles. In particular, it is preferable to use a liquid containing fine bubbles. The details of the liquid containing fine bubbles are the same as the liquid containing fine bubbles (reaction liquid) used in the particle preparation step. Further, it is preferable that the metal particle dispersion liquid produced after cleaning also contains fine bubbles.

By cleaning the metal particles with a cleaning liquid containing fine bubbles, ionization and oxidation of the metal particles are prevented, and the storage stability of the metal particle dispersion liquid and the pot life of the coating liquid using this metal particle dispersion liquid are dramatically improved. Can be improved. In addition, the dispersibility of the produced metal particles is improved, and the amount of organic substances derived from salts and organic stabilizers in the final dispersion can be reduced. Therefore, when the film is formed, the metal particles come into direct contact with each other, the resistance at the particle boundary is reduced, and as a result, a film having high conductivity can be formed.

Examples of the cleaning method include an ultrafiltration membrane method and a decantation method. Impure components such as nitrate ion and sulfate ion can be removed by washing. Further, it is preferable to purify using an ion exchange resin.

When a liquid containing fine bubbles is used, the impure component can be sufficiently removed, and the subsequent treatment with an ion exchange resin can be simplified (reduction of the amount of resin), so that metal particles can be efficiently produced. It is also possible to reduce the number of washings, which also enables efficient production of metal particles. By simplifying the cleaning process as described above, the loss of metal particles can be reduced and the yield can be improved. Further, since the induction of oxidation of the metal particles is suppressed by the simplification of the cleaning step, the coating film formed by using the metal particles has high conductivity.

<Coarse particle removal process>
After the washing step, it is preferable to remove the coarse particles by centrifugation or the like.

The present invention also relates to a metal particle dispersion prepared by the above-mentioned production method. This will be described below.
[Metal particle dispersion]
The metal particle dispersion liquid of the present invention is characterized in that metal particles are dispersed in a liquid containing fine bubbles. The details of the liquid containing fine bubbles are the same as the liquid containing fine bubbles (reaction liquid) used in the particle preparation step. Examples of the metal particles include metal particles of groups 4, 5, 6, 8, 9, 10, 11, 11, 13, 14, and 15 of the periodic table. A plurality of types of metal particles may be mixed and used. This metal particle dispersion can be produced by the above-mentioned production method.
Water or an organic solvent is suitable as the dispersion medium. Here, the organic solvent is not particularly limited in type, but alcohols are preferable, and methanol and ethanol are more preferable because of the ease of processing as a coating liquid and the ease of producing a coated substrate.

The storage stability of the metal particle dispersion is usually about several hours to one month, although it depends on the metal species when it is produced using only a solvent bubbled with an inert gas. On the other hand, the storage stability of the metal particle dispersion of the present invention exceeds 3 months. It is considered that this is because some action is acting between the fine bubbles and the metal particles, which is different from the action when the bubbles are simply present.

With the current technique, it is difficult to measure the average bubble diameter and the number of bubbles of the fine bubbles in the dispersion liquid in which the metal particles and the fine bubbles coexist. Therefore, the metal particles are removed with an ultrafiltration membrane, and the fine bubbles contained in this filtrate are measured to obtain the average bubble diameter and the number of fine bubbles. That is, the average bubble diameter and the number of bubbles of the present invention refer to those obtained by measuring a filtrate that has passed through an ultrafiltration membrane having a molecular weight cut-off of 4000.

The redox potential (ORP) of the metal particle dispersion is preferably 0 to 300 mV, more preferably 100 to 250 mV. Here, when the ORP is less than 0 mV, the dispersibility of the metal particles may become unstable because it is in the reducing field. On the contrary, when the ORP exceeds 300 mV, the metal particles may be oxidized.
The pH is usually 4.0 to 7.0, preferably 4.5 to 6.5. Here, when the pH is less than 4.0, it exists in an ionic state, and metal particles may not be obtained. On the contrary, when the pH exceeds 7.0, the metal particles may aggregate due to the high salt concentration.

The electrical conductivity of the metal particle dispersion is preferably 10 to 500 μS / cm, more preferably 50 to 300 μS / cm. Here, when the electric conductivity is less than 10 μS / cm, the amount of the dispersant may be small and the storage stability may be lowered (the life may be short). On the contrary, when the electric conductivity exceeds 500 μS / cm, the salt concentration becomes high, so that the storage stability may decrease. Further, even if a conductive film is formed, the conductivity may deteriorate.

The content of each of the impure components of the metal particle dispersion is preferably 100 ppm or less, more preferably 80 ppm or less, still more preferably 50 ppm or less, based on the metal particles. Here, if it exceeds 100 ppm, the salt concentration becomes high, so that the storage stability may decrease. Further, even if a conductive film is formed, the conductivity may deteriorate. The impure content of the metal particle dispersion is a substance other than the metal particles, the dispersion medium and the organic stabilizer. This is a substance other than the metal particles generated by the reduction treatment of the metal salt, and exists as an ion in the reaction solution. Specifically, metal ions such as sodium and iron, boron ions, chloride ions, nitrate ions, sulfate ions and the like are exemplified. In particular, the metal ions of sodium and iron preferably satisfy both sodium of 10 ppm or less and iron of 50 ppm or less in terms of conductivity.

The carbon content of the metal particles contained in the metal particle dispersion is preferably 0.1% by mass or less, more preferably 0.05% by mass or less with respect to the metal particles.
The carbon contained in the metal particles is derived from an organic compound such as a metal salt, a reducing agent, a pH adjuster, a cleaning solution, or a solvent. This includes those intentionally added for the production of metal particle dispersions, as well as those inevitably present in raw materials and the like. In particular, if the metal particle dispersion liquid contains the above-mentioned organic stabilizer, the surface of the metal particles is coated with an organic substance, and therefore, when the metal particle dispersion liquid is formed into a film, the conductivity may decrease. The carbon content derived from such an organic substance can be determined by analyzing the C (carbon) content as described later.

The average particle size of the metal particles contained in this metal particle dispersion is preferably 3 to 200 nm, more preferably 5 to 70 nm. When the average particle size is 3 to 200 nm, a highly transparent conductive film can be obtained.
The average particle size of the metal particles is obtained by taking an electron micrograph, measuring the particle size of any 500 particles, and obtaining the average value thereof.

The metal particle dispersion liquid of the present invention can suppress oxidation and ionization of metal particles. Therefore, even in an aqueous system, long-term storage stability that could not be realized in the past can be realized. In addition, a long-term pot life that could not be realized in the past can be realized even with a coating liquid using this metal particle dispersion liquid. Further, this metal particle dispersion liquid has a very low content of oxide particles, and can produce a highly conductive film. Here, the metal oxide in the metal particle dispersion can be confirmed by X-ray diffraction. It is preferable that this metal oxide is not detected by X-ray diffraction. The content thereof is preferably 500 ppm or less, more preferably 200 ppm or less, still more preferably 100 ppm or less with respect to the particles. If the content of the metal oxide exceeds 500 ppm, the storage stability of the dispersion liquid is lowered, and the particles may aggregate and precipitate. Further, when the metal particles are ionized, they do not exist as particles in the liquid, and even if they are used as a coating liquid, a desired film cannot be obtained.

The present invention also relates to a method for producing a coated base material, which comprises applying a coating liquid using the above-mentioned metal particle dispersion liquid onto a base material. These will be described below.
[Manufacturing method of coating liquid]
A coating liquid for forming a film can be produced using the metal particles contained in the metal particle dispersion liquid of the present invention. Various conventionally known additives can be added to the coating liquid for film formation.

[Manufacturing method of coated substrate]
In the production of a coated base material, this coating liquid is applied onto the base material, dried, and fired if necessary.

Examples of the base material include film-like and sheet-like base materials made of glass, plastic, ceramic, metal and the like. Examples of the coating method of the coating liquid include a dipping method, a spinner method, a spray method, a roll coater method, and a flexographic printing method. The film thickness of the film is preferably about 30 to 300 nm, more preferably about 50 to 200 nm.

The drying temperature is, for example, a temperature of about room temperature to 90 ° C. The firing temperature is, for example, about 120 to 900 ° C., and may be about 150 to 350 ° C. Since the metal particles contained in the dispersion liquid of the present invention have a low carbon content of 0.1% by mass or less with respect to the metal particles, the adhesion of organic substances such as an organic stabilizer is small, so that they are fired at a high temperature such as 400 ° C. or higher. There is no need to remove organic matter. As a result, it is possible to prevent aggregation and fusion of metal particles due to high-temperature firing, and it is possible to suppress deterioration of the haze of the obtained film.

Next, a method for producing the metal particle dispersion liquid of the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[Example 1]
<Particle preparation process>
N ₂ micro _- nano bubble water (average bubble diameter 70 nm, number of bubbles 240 million cells / mL) is brought into contact with ultrapure water using a swirling flow type bubble generator (HYK-20-SD manufactured by Ligaric Co., Ltd.). , PH 5.79, electrical conductivity 1.17 μS / cm, DO 1.70 ppm, ORP330 mV).
180 g of ferrous sulfate heptahydrate was dissolved in 600 g of _N2 micro-nano bubble water to prepare a solution A1.

76 g of copper (II) nitrate trihydrate was dissolved in 600 g of _N2 micro-nano bubble water to prepare a solution B1. Then, the solution A1 was added to the solution B1 and stirred for 10 hours, and the metal particles were separated and recovered from the obtained dispersion by a centrifuge.

<Washing process>
_N2 micro-nano bubble water was prepared in the same manner as in the particle preparation step.
The metal particles separated and recovered were immersed in 200 g of _N2 micro-nano bubble water, washed (demineralized), and then separated and recovered by centrifugation again.

<Preparation of metal particle dispersion>
The metal concentration of the separated and recovered metal particles was quantified by ICP analysis, and an aqueous dispersion of metal particles having a concentration of 2.5% by mass in terms of metal was prepared using N ₂ micro-nano bubble water. Then, deionization was performed using 10 g of an amphoteric ion exchange resin to obtain a black-brown metal particle dispersion P1 having a concentration of 2.5% by mass in terms of metal.

[Average bubble diameter and number of microbubbles]
For the fine particles in the metal particle dispersion P1, the metal particle dispersion is filtered through an ultrafiltration membrane (SEP-1013 fractional molecular weight 4000 manufactured by Asahi Kasei) to remove the metal particles, and the average bubbles of the fine particles in the filtrate are averaged. The diameter and the number of bubbles were measured. The average bubble diameter and the number of bubbles of the fine bubbles were measured by measuring the Brownian motion moving speed of the bubbles in the liquid by using the nanoparticle tracking analysis method. Specifically, about 20 mL of the measurement sample (solution A1, solution B1 or metal particle dispersion P1 filtrate) is sucked and injected into a measuring instrument (“Nanosite NS300” manufactured by Malvern) for nanoparticle tracking analysis method. Was measured. The micro-nano bubble water was measured by the above method as it was without filtration treatment.

Physical characteristics of the solution after reduction in the particle preparation step (pH, ORP), physical properties of the finally obtained metal particle dispersion (pH, ORP, yield of metal particles, average bubble diameter and number of fine bubbles, metal Average particle size of primary particles, average particle size of secondary metal particles, content of metal particles (metal concentration), amount of C (carbon), impure content (Na, Fe, Na, B, SO ₄ , NO ₃ ) ) Content) is shown in Table 1. Table 2 shows the presence or absence of metals and metal oxides in the metal particle dispersion and the storage stability of the metal particle dispersion (the same applies to the following Examples and Comparative Examples).

[Electrical conductivity]
The electrical conductivity was measured by the AC two-electrode method. Specifically, a pH meter (F-74 manufactured by HORIBA, Ltd., electrode model number 3551-10D) was obtained by immersing the electrode in the liquid to be measured in the conductivity measurement mode. The temperatures of the bubbling water, the micro-nano bubble water, and the metal particle dispersion were adjusted to 25 ° C.

[Redox potential (ORP)]
The oxidation-reduction potential (Oxidation Reduction Potential) was determined by immersing the electrode in a liquid for measuring the electrode in the ORP measurement mode for setting the pH meter (F-74 manufactured by Horiba Seisakusho, electrode model number 9300-10D). The temperatures of the bubbling water, the micro-nano bubble water, and the metal particle dispersion were adjusted to 25 ° C.

[Dissolved oxygen concentration (DO)]
Dissolved Oxygen concentration was measured by the septal galvanic cell method. Specifically, a pH meter (OM-51 manufactured by HORIBA, Ltd., electrode model number 9520-10D) was obtained by immersing the electrode in the liquid to be measured in the conductivity measurement mode under atmospheric pressure. The temperatures of the bubbling water, the micro-nano bubble water, and the metal particle dispersion were adjusted to 25 ° C.
[Particle yield]
The yield of metal particles is calculated by calculating the amount of metal in the metal particle dispersion from the metal concentration in the metal dispersion measured by ICP, and dividing this by the theoretical amount of metal calculated from the charged metal salt. Was multiplied by 100.

[Average particle size of primary particles]
The average particle size of the metal particles was measured by an image analysis method. Specifically, the metal particle dispersion is dried on a collodion film of a copper cell for an electron microscope by a transmission electron microscope (H-800 manufactured by Hitachi, Ltd.), and a photograph is taken at a magnification of 250,000 times. The particle size of any 500 particles in the obtained photographic projection was measured, and the average value was taken as the average particle size of the metal particles.

[Average particle size of secondary particles]
The metal particle dispersion was placed in the cell as it was, measured by the microtrac method, and the average value (D50) was taken as the average particle diameter of the metal particles.

[ICP analysis]
Mass spectrometry of each element was performed by chemical analysis using an inductively coupled plasma spectrophotometer. Specifically, a solution prepared by dissolving a metal particle dispersion in concentrated nitric acid and adjusting the concentration to 10 to 100 mass ppm with water was analyzed by SEQUENTIAL PLASMA SPECTROMETER (ICPS-8100) manufactured by Shimadzu Corporation.

[Measurement of C (carbon) amount]
The carbon content in the metal particles was measured by drying the metal particle dispersion at 100 ° C. and using a carbon sulfur analyzer (EMIA-320V manufactured by HORIBA).

[Ion chromatographic analysis]
The metal particle dispersion was diluted 100-fold with ultrapure water, and the concentrations of SO ₄ and NO ₃ were measured using an ion exchange chromatograph (TSKgel SuperQ-5PW manufactured by Tosoh).

[Confirmation of the presence or absence of metal oxides by X-ray diffraction]
The metal particle dispersion was analyzed by X-ray diffraction with the solution as it was, and the presence or absence of the metal oxide was confirmed. The qualitative analysis of the sample by X-ray diffraction was performed by X-RAY DIFFRACT METER (SmartLab) manufactured by RIGAKU Co., Ltd. Specifically, the sample is placed in a cell, set in a device, tube voltage 45.0 kV, tube current 200.0 mA, anti-cathode Cu, measurement range: start angle to end angle (2θ) 5.000 ° to 70.000. The measurement was performed at ° and a scan speed of 5.000 ° / min.
If no metal oxide peak is observed: ○
When a peak of metal oxide is observed: ×

[Storage stability]
The presence or absence of oxidation of the metal particles and the change in conductivity by X-ray diffraction (XRD) of the metal particle dispersion stored at 25 ° C. were confirmed.

<Preparation of coating liquid and coated base material>
The obtained metal particle dispersion P1 was diluted with ethanol to 0.5% by mass to prepare a coating liquid. This was applied to glass by a spin coating method, and then fired at 200 ° C. for 30 minutes in a nitrogen atmosphere to prepare a coated substrate. The conductivity (surface resistance) of this coated substrate was measured with a low resta (NSCP probe manufactured by Mitsubishi Chemical Corporation). In addition, a part of the coating film was peeled off with a cutter knife to create a step, and this step was measured with a laser microscope, and this was used as the film thickness. These results are shown in Table 2 (the same applies to the following examples and comparative examples).

[Example 2]
<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
In the washing step of Example 1, 200 g of a 20 mass% 3 sodium citrate aqueous solution prepared using N ₂ micro-nano bubble water was used instead of N ₂ micro-nano bubble water in the same manner as in Example 1. , A black-brown metal particle dispersion P2 was obtained.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid P2 was used instead of the metal particle dispersion liquid P1.

[Example 3]
<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
Bubbling ultrapure water (pH (25 ° C., same hereafter) 6.32, electrical conductivity 0.05 μS / cm, dissolved oxygen amount (DO) 6.17 ppm, redox potential (ORP) 350 mV) with _N2 . After 1 hour, N ₂ bubbling water (pH 6.6, electrical conductivity 0.6 μS / cm, DO 0.6 ppm, ORP 260 mV) from which dissolved oxygen was removed was prepared.
In the washing step of Example 1, a black-brown metal particle dispersion P3 was obtained in the same manner as in Example 1 except that N ₂ bubbling water was used instead of N ₂ micro-nano bubble water.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid P3 was used instead of the metal particle dispersion liquid P1.

[Example 4]
<Particle preparation process>
100 g of ferrous sulfate heptahydrate was dissolved in 500 g of N ₂ micro-nano bubble water to prepare a solution A4.

57 g of silver nitrate (I) was dissolved in 300 g of _N2 micro-nano bubble water to prepare a solution B4. Then, the solution A4 was added to the solution B4, and the metal particles were separated and recovered from the dispersion obtained by stirring for 10 hours by a centrifuge.

<Washing process>
The metal particles separated and recovered were immersed in 200 g of an aqueous solution of 3 sodium citrate having a concentration of 20% by mass prepared using _N2 micro-nanobubble water, washed (demineralized), and then separated and recovered by centrifugation again.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
A black-brown metal particle dispersion P4 was obtained in the same manner as in Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid P4 was used instead of the metal particle dispersion liquid P1.

[Example 5]
<Particle preparation process>
50 g of nickel nitrate hexahydrate (Ni (NO ₃ ) _{26H 2 O} ) (manufactured by Kanto Chemical Co., Ltd.) was dissolved in 450 g of N ₂ micro-nano bubble water to prepare a solution A5.

50 g of sodium borohydride (reducing agent) was dissolved in 1000 g of N ₂ micro-nano bubble water to prepare a solution B5. While stirring the solution A5, the solution B5 was added and stirred for 1 hour. At this time, the liquid changed from green to black. Metal particles were separated and recovered from the obtained dispersion by a centrifuge.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
A black metal particle dispersion P5 was obtained in the same manner as after the washing step of Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid P5 was used instead of the metal particle dispersion liquid P1.

[Example 6]
<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
Solution B6 was prepared by dissolving 9.1 g of palladium (II) nitrate dihydrate in 600 g of N ₂ micro-nano bubble water.
A black-brown metal particle dispersion P6 was obtained in the same manner as in Example 1 except that solution B6 was used instead of solution B1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid P6 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 1]
<Particle preparation process>
_N2 bubbling water was prepared in the same manner as described in the washing step of Example 3.
400 g of trisodium citrate dihydrate (organic stabilizer) was dissolved in 930 g of _N2 bubbling water to prepare a solution (RS1-1).
180 g of ferrous sulfate heptahydrate (reducing agent) was dissolved in 600 g of _N2 bubbling water to prepare a solution (RS1-2).
The solution (RS1-1) and the solution (RS1-2) were mixed and stirred for 30 minutes to prepare solution RA1.

76 g of copper (II) nitrate trihydrate was dissolved in 600 g of _N2 bubbling water to prepare a solution RB1. Then, the solution RA1 was added to the solution RB1 and stirred for 10 hours, and the metal particles were separated and recovered from the obtained dispersion by a centrifuge.

<Washing process>
The metal particles separated and recovered were immersed in 200 g of an aqueous solution of 3 sodium citrate having a concentration of 20% by mass prepared using _N2 bubbling water, washed (demineralized), and then separated and recovered by centrifugation again.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
A black-brown metal particle dispersion RP1 was obtained in the same manner as in Example 1 except that N ₂ bubbling water was used instead of N ₂ micro-nano bubble water.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP1 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 2]
<Particle preparation process>
Metal particles were separated and recovered from the dispersion obtained in the same manner as in Example 1 except that N ₂ bubbling water was used instead of N ₂ micro-nano bubble water by a centrifuge.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
After the washing step, a black-brown metal particle dispersion RP2 was obtained in the same manner as in Comparative Example 1.
However, this dispersion immediately settled, and it was not possible to prepare a coating liquid and a coated base material.

[Comparative Example 3]
<Particle preparation process>
400 g of trisodium citrate dihydrate was dissolved in 930 g of _N2 bubbling water to prepare a solution (RS3-1).
A solution (RS3-2) was prepared by dissolving 100 g of ferrous sulfate heptahydrate in 500 g of _N2 bubbling water.
The solution (RS3-1) and the solution (RS3-2) were mixed and stirred for 30 minutes to prepare solution RA3.

Metal particles were separated from the dispersion obtained in the same manner as in Example 4 except that solution RA3 was used instead of solution A4 and N ₂ bubbling water was used instead of N ₂ micro-nano bubble water by a centrifuge. Collected.

<Washing process>
The metal particles separated and recovered were immersed in 200 g of an aqueous solution of 3 sodium citrate having a concentration of 30% by mass prepared using _N2 bubbling water, washed (demineralized), and then separated and recovered by centrifugation. Next, the metal particles separated and recovered were immersed in 200 g of an aqueous solution of 3 sodium citrate having a concentration of 20% by mass, which was similarly prepared using _N2 bubbling water, washed (demineralized), and then separated and recovered by centrifugation again. did.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
A black-brown metal particle dispersion RP3 was obtained in the same manner as in Comparative Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP3 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 4]
<Particle preparation process>
N ₂ bubbling water 450 g, nickel nitrate hexahydrate (Ni (NO ₃ ) _{26H 2 O} ) (manufactured by Kanto Chemical Co., Ltd.) 50 g, citric acid hydrate (organic stabilizer) (Kishida Chemical Co., Ltd.) )) 0.5 g was dissolved to prepare a solution RA4.

The same procedure as in Example 5 was carried out except that solution RA4 was used instead of solution A5 and _N2 bubbling water was used instead of _N2 micro-nano bubble water. At this time, the liquid changed from green to black. Metal particles were separated and recovered from the obtained dispersion by a centrifuge.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
After the washing step, a black metal particle dispersion RP4 was obtained in the same manner as in Comparative Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP4 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 5]
<Particle preparation process>
A solution RA5 was prepared in the same manner as the solution RA1 of Comparative Example 1.

Metal particles were centrifuged from the dispersion obtained in the same manner as in Example 6 except that solution RA5 was used instead of solution A6 and N ₂ bubbling water was used instead of N ₂ micro-nano bubble water. Separated and recovered.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
After the washing step, a black-brown metal particle dispersion RP5 was obtained in the same manner as in Comparative Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP5 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 6]
<Particle preparation process>
Particles were prepared in the same manner as in Comparative Example 1 except that N ₂ micro-nano bubble water was used instead of N ₂ bubbling water.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
After the washing step, a black-brown metal particle dispersion RP6 was obtained in the same manner as in Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP6 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 7]
<Particle preparation process>
Particles were prepared in the same manner as in Comparative Example 1 except that N ₂ micro-nano bubble water was used instead of N ₂ bubbling water.

<Washing process>
The same as in Comparative Example 1.

<Preparation of metal particle dispersion and preparation of coated substrate>
A black-brown metal particle dispersion RP7 was obtained in the same manner as in Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP7 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 8]
<Particle preparation>
Particles were prepared in the same manner as in Comparative Example 1.

<Washing process>
The same procedure as in Comparative Example 1 was carried out except that N ₂ micro-nano bubble water was used instead of N ₂ bubbling water.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
A black-brown metal particle dispersion RP8 was obtained in the same manner as in Comparative Example 1. A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP8 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 9]
<Particle preparation>
Particles were prepared in the same manner as in Comparative Example 2.

<Washing process>
The same procedure as in Comparative Example 1 was carried out except that N ₂ micro-nano bubble water was used instead of N ₂ bubbling water.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
A black-brown metal particle dispersion RP9 was obtained in the same manner as in Example 1.
However, this dispersion immediately settled, and it was not possible to prepare a coating liquid and a coated base material.

[Comparative Example 10]
<Particle preparation process>
_N2 micro-nano bubble water was prepared in the same manner as in Example 1.
400 g of trisodium citrate dihydrate was dissolved in 930 g of N ₂ micro-nano bubble water to prepare a solution (RS10-1).
A solution (RS10-2) was prepared by dissolving 100 g of ferrous sulfate heptahydrate in 500 g of _N2 micro-nanobubble water.
The solution (RS10-1) and the solution (RS10-2) were mixed and stirred for 30 minutes to prepare a solution RA10.
Metal particles were separated and recovered by a centrifuge from the dispersion obtained in the same manner as in Example 4 except that the solution RA10 was used instead of the solution A4.

<Washing process>
The same procedure as in Comparative Example 3 was carried out except that N ₂ micro-nano bubble water was used instead of N ₂ bubbling water.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
A black-brown metal particle dispersion RP10 was obtained in the same manner as in Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP10 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 11]
<Particle preparation process>
The same procedure as in Comparative Example 4 was carried out except that N ₂ micro-nano bubble water was used instead of N ₂ bubbling water. At this time, the liquid changed from green to black. Metal particles were separated and recovered from the obtained dispersion by a centrifuge.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
After the washing step, a black metal particle dispersion RP11 was obtained in the same manner as in Example 1. A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP11 was used instead of the metal particle dispersion liquid P1.

[Comparative Example 12]
<Particle preparation process>
Metal particles were separated and recovered from the dispersion obtained in the same manner as in Comparative Example 5 by a centrifuge, except that N ₂ micro-nano bubble water was used instead of N ₂ bubbling water.

<Preparation of metal particle dispersion liquid, preparation of coating liquid and coated substrate>
After the washing step, a black-brown metal particle dispersion RP12 was obtained in the same manner as in Example 1.
A coating liquid and a coated base material were prepared and evaluated in the same manner as in Example 1 except that the metal particle dispersion liquid RP12 was used instead of the metal particle dispersion liquid P1.

Since the metal particle dispersion liquid of the present invention can be used for forming a conductive film or the like, it is industrially useful.

Claims (5)

The process of reducing metal salts in a liquid that does not contain an organic stabilizer to prepare metal particles, and
The step of cleaning the metal particles and
Have,
A method for producing a metal particle dispersion liquid, which comprises microbubbles having an average bubble diameter of 40 nm to 10 μm and made of at least one non-oxidizing gas of nitrogen and a rare gas in the liquid. The metal particle dispersion according to claim 1 , wherein the cleaning liquid used for the cleaning is at least one of a bubbling liquid from which oxygen has been removed by bubbling an inert gas in advance and a liquid containing the fine bubbles. Liquid manufacturing method. Claim 1 characterized in that the metal salt is a metal salt selected from Group 4, Group 5, Group 6, Group 8, Group 9, Group 10, Group 11, Group 13, Group 14, and Group 15. Alternatively, the method for producing a metal particle dispersion liquid according to 2. A step of preparing a coating liquid containing metal particles by using the metal particle dispersion liquid prepared by the method according to any one of claims 1 to 3.
The process of applying the coating liquid on the substrate to form a film, and
A method for producing a coated base material, which comprises. The metal particles are dispersed in a liquid containing microbubbles composed of at least one non-oxidizing gas of nitrogen and a rare gas having an average bubble diameter of 40 nm to 10 μm, and have a redox potential of 0 to 300 mV. A metal particle dispersion having a carbon content of 0.1% by mass or less.